Some material processing apparatus include a rotor to which an operator may be exposed, particularly during maintenance, thereby risking injury or death. For example, an impact crusher includes a rotatable drum spaced apart from a crushing wall. In use, the rotating action of the drum bounces rocks against the crushing wall until they are small enough to fit through a gap beside the drum. If the crusher jams the operator has to open the crusher to clear the jam. Should the drum rotate when the crusher is open, rocks may be flung from the crusher causing injury, or the operator may become trapped by the drum. In some instances, it is necessary to manually rotate the drum in order to free a blockage or for other maintenance purposes, e.g. replacing a wearable component such as a blade. Operators have been known to stand on the drum to try to rotate it with their weight and this may result in injury or death.
It would be desirable therefore to provide an apparatus in which unwanted rotation of the rotor is prevented while still allowing purposeful rotation.